Inflammation is an important part of normal pulmonary host-defense processes, but when the control of inflammation is compromised and the response too exuberant, the consequences for the lung can be deadly. The alveolar macrophage plays a central role in triggering an regulating the inflammatory response and we will examine the ability of pulmonary surfactant to regulate macrophage differentiation and function. This regulation depends on a delicate balance between the usually dominant inhibitory effects of surfactant lipids and the stimulatory influence of SP-A, a protein whose levels increase during many types of lung injury. We will use the THP-1 monocytic cell line and normal monocytes and alveolar macrophages to test the hypotheses that surfactant is responsible for development and maintenance of the distinct phenotype of the alveolar macrophage and that SP-A and surfactant containing higher than normal amounts of SP-A can alter macrophage phenotype, promoting the development of an inflammatory response. Specific Aim 1 will use flow cytometry to define the effects that surfactant components exert on the expression of macrophage cell surface molecules and RT-PCR to assess mRNA levels for these markers. Specific Aim 2 will study the effect of SP-A on the production of the proinflammatory cytokines (TNF-alpha, IL- 1beta, IL-6 and IL-8) and the modulation of this influence by surfactant lipids. Cytokines will be measured by ELISA and mRNA by RT-PCR. The mechanism responsible for these actions will be probed with neutralizing antibodies and by the addition of exogenous cytokines. Specific Aim 3 will use biochemical techniques to identify proteins on the macrophage cell surface that serve as ligands for SP-A and the conditions needed for binding to occur. The results of this work will provide valuable insight into how the alveolar microenvironment controls the ability of the alveolar macrophage to initiate and modulate an inflammatory response in the lung. The information gained will serve as a basis for the development of new therapeutic modalities to prevent and halt lung inflammation and reduce the significant morbidity and mortality associated with it.